Hi Donald - Ubuntu is based on a snapshot of Debian unstable (Sid), 64 Studio 2.0 is based on an official release of Debian stable (Etch). So mixing these two sources is certain to cause dependency problems. Here are the sources you should use, in the file /etc/apt/sources.list.d/64studio.list
# Stable 64 Studio repository
deb http://apt.64studio.com/64studio/stable/ 64studio main
# Debian etch
deb http://ftp.debian.org/debian/ etch main
# Security updates
deb http://security.debian.org/ etch/updates main
# Bleeding edge 64 Studio repository, only for testers!
# deb http://apt.64studio.com/64studio/testing/ 64studio main
Notice I have the Etch and security sources uncommented so I can get extra packages from Debian.

The debian world is quite big, and there are lots and lots of small debian repos out there.
The most important ones for use in 64studio are already listed in Synaptic.
The others are not officially recommended (because of some license issues) and are therefore your own choice. Some of the more unstable repos might also break your machine, as the maintainers of those do not always test the software properly before posting.
The easiest way to find a specific repo is to do an internet search with the application name and debian in the search field. Just know this is only for the adventurous (like me) and could be dangerous. MAKE BACKUPS OF YOUR DATA.
Hope it helps (without helping too much unfortunately)